The problem
I can't find the reason Swagger doesn't show the POST end point with the textarea 'body' available so I can paste JSON into.
I expected to see a page like this the POST in PetStore Swagger
But my form is simply posted after I click 'Try it out' and I get
Response Body
    <html>
      <head>
        <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"/>
        <title>Error 415 Unsupported Media Type</title>
      </head>
      <body><h2>HTTP ERROR 415</h2>
        <p>Problem accessing /promotions. Reason:
          <pre>    Unsupported Media Type</pre></p><hr><i><small>Powered by Jetty://</small></i><hr/>
      </body>
    </html>
Response Headers
{
  "access-control-allow-origin": "http://localhost:8080",
  "date": "Thu, 11 Jun 2015 07:37:15 GMT",
  "cache-control": "must-revalidate,no-cache,no-store",
  "access-control-allow-credentials": "true",
  "content-type": "text/html; charset=ISO-8859-1",
  "content-length": "320",
  "access-control-expose-headers": ""
}
Can you help me with this please?
More information on my project
$ java -version
java version "1.8.0_45"
Java(TM) SE Runtime Environment (build 1.8.0_45-b14)
Java HotSpot(TM) 64-Bit Server VM (build 25.45-b02, mixed mode)
Maven
parent
    - pom.xml:   <dropwizard.version>0.8.1</dropwizard.version>
                 <swagger.version>0.7.0</swagger.version>)
  app
    - pom.xml:   <dependency>
                    <groupId>io.dropwizard</groupId>
                    <artifactId>dropwizard-core</artifactId>
                    <version>${dropwizard.version}</version>
                 </dependency>
                 <dependency>
                    <groupId>io.federecio</groupId>
                    <artifactId>dropwizard-swagger</artifactId>
                    <version>${swagger.version}</version>
                 </dependency>
    - config.yml: 
                 swagger:
                   resourcePackage: myproject.promotion.v1.resource             
  representation
    - pom.xml
Configuration
package myproject.promotion.app.config;
public class PromotionServiceConfiguration extends Configuration {
    @JsonProperty("swagger")
    public SwaggerBundleConfiguration swaggerBundleConfiguration;    
}
Application
package myproject.promotion.app;
public class PromotionServiceApplication extends Application<PromotionServiceConfiguration> {
public static void main(String[] args) throws Exception {
    new PromotionServiceApplication().run(args);
}
@Override
public void initialize(Bootstrap<PromotionServiceConfiguration> bootstrap) {
    bootstrap.addBundle(new PromotionSwaggerBundle());
}
@Override
public void run(PromotionServiceConfiguration configuration, Environment environment) {
//Deleted to make it short
}
}
PromotionSwaggerBundle
package myproject.promotion.app.config;
public class PromotionSwaggerBundle extends SwaggerBundle<PromotionServiceConfiguration> {
@Override
protected SwaggerBundleConfiguration getSwaggerBundleConfiguration(PromotionServiceConfiguration configuration) {
    return configuration.swaggerBundleConfiguration;
}
}
End point
package myproject.v1.resource;
@Path("/promotions")
@Api(value = "/promotions/", description = "Promotions' possible operations", consumes = "application/json", produces = "application/json")
public class PromotionManagementResource {
    private static final String PROMO_PARAM = "promotionId";
    private final PromotionManagementService promotionManagementService;
    @Inject
    public PromotionManagementResource(PromotionManagementService promotionManagementService) {
        this.promotionManagementService = promotionManagementService;
    }
    @POST
    @Consumes(APPLICATION_JSON)
    @ApiOperation(value = "Create promotion")
    @ApiResponses(value = {
            @ApiResponse(code = 201, message = "Promotion created. Link to it in Location HEADER"),
            @ApiResponse(code = 409, message = "Promotion already exists")
            })
    public Response create(final Promotion promotion, @Context final UriInfo uriInfo) throws IOException {
        Promotion createdPromotion = promotionManagementService.create(promotion);
        URI createdInventoryURI = inventory(createdPromotion, uriInfo);
        return Response.created(createdInventoryURI).build();
    }
				
                        
In the end the annotation @ApiParam did the trick.
New POST method (with the new annotation)
Thanks for your help cyrbil.